When wild hogs roamed the forest in sparse numbers with the population determined by the available food sources, the environmental impact of the hog excretion was insignificant. The individual animal roamed freely, spreading his waste over large areas as he traveled. Later, when man domesticated hog and other livestock, and increased the local concentration to correspond to the caretakers food production, the environmental impact of waste was at first minimal. The farmer removed the waste manure from the pig sty and spread it over his farm for fertilizer.
In recent times, however, livestock production density has dramatically increased. For example, the speciality hog production operators purchased their hog feed (cereal grains) from other farmers who specialized in the production of grain cereal. This enables one operator to have the hog production facility of 100,000 head of hogs or more. The production of hog manure now becomes a problem. The spreading of large quantities of hog manure on land requires an extensive amount of land. The soil has a finite capacity to degrade animal feces, and when exceeded it becomes the equivalent of a pile of manure.
In addition to the practical limits of the distribution of animal feces, regulatory agencies have applied limits to the amount of animal feces per acre to be approximately equivalent to the plant uptake of the non-biodegradable components. The regulations were created to prohibit the surface run-off from storm water and the excess percolation of the soluble waste components into the ground water.
In recent times, livestock producers have elected to create pits or lagoons for the collection of the waste. In the barns or houses, the animals live on elevated flooring which permits the feces to drop through the floor to a sub-floor. This sub-floor is periodically flushed to remove the feces and maintain a healthy living environment. The feces with the wash down water as a vehicle flow to the storage lagoon.
A properly operated lagoon will biologically decompose a significant amount of the animal waste. However, large amount production operations require proportionately large lagoons and therefore a significant amount of land is consumed. Also, the two major components of animal waste that are regulated, mainly nitrogen and phosphorous, are not significantly removed by a stagnant lagoon or pond.
When the lagoon-treated waste is applied to the crop land it contains high levels of nitrogen and phosphorous. The regulatory limit for the land application of nitrogen is proportionate to the amount of nitrogen consumed by the crop produced. The regulatory level of nitrogen consumed by hay is approximately two (2) times the amount of corn and four (4) times the level for cotton (hay--250 lbs/acre of nitrogen, corn--100 lbs/acre of nitrogen, cotton--60 lbs/acre of nitrogen). In most areas hay has very little resale value and is not an economically advantageous crop to produce. Corn is near break even. Cotton, however is an economical cash crop and hence the most desirable to the farmers. The disadvantage is that the amount of land required to properly apply the waste nitrogen is four (4) times the level of hay. Hence, if the farmers can reduce the levels of nitrogen in the irrigation water, he can economically produce cotton.
With a low nitrogen concentration, the farmer may apply a much larger volume of water per acre without exceeding the maximum nutrient level. In some cases the quantity of water may be increased by a factor of 40 times. This dramatically reduces the labor required to move and maintain the sprinkler irrigation system.
The water utilized to flush the livestock production floor and move the freshly produced feces to the lagoon is usually recycled from the pond. Recycling the wastewater provides two advantages to the producer. First, it reduces that amount of fresh water that must be provided and secondly since it is recycled from the pond, the size of the pond can be significantly smaller.
The problem with the recycled water is that it contains high level of ammonia (breakdown product of the waste urea) and odors which are not beneficial to the health of the livestock. High levels of ammonia in the flush water require the building to be vented to reduce the ambient levels of ammonia. Increased ventilation lowers the ambient temperatures in the winter, lowers the rate of weight gain of the animal, and increases the food input of the animal to maintain body temperature.
The wastewater treatment facility of the present invention is simple. It does not require any chemicals to precipitate soluble nitrogen and organic compounds. There is no skimming of the bio-cultures required to maintain biological activity. The wastewater treatment facility of the present invention includes biological cultures of anoxic, anaerobic and aerobic conditions.
Biological cultures purify water by exploiting the metabolic processes of various bacterial and algal species to convert organic and inorganic waste products into benign end products, typically carbon dioxide and more cells. Intermediate products formed by biological processes, however, can include methane and sulfur gases or other volatile or odiferous products, depending on the nature of the culture and the waste material being digested. Biological cultures can be fostered of desirable microorganisms which provide the functional basis for the wastewater treatment by metabolically converting the waste products. Cultures of undesirable microorganisms which produce undesirable tastes, odors, growths, or which are actually toxic are also possible, however, and it is important in biological wastewater treatment that cultures of suitable microorganisms be fostered and that undesirable cultures be avoided.
The organic material in the wastewater serves both as an energy source and a source of carbon for cell synthesis by the microorganisms of the culture. Microorganisms are both reactants and products in the biological treatment of wastewater. Typical configurations of biological reactor cultures for purifying water include suspended-culture processes and attached growth systems such as film-flow reactors. Suspended cultures include activated sludge (flocculent cultures), aerated lagoons, oxidation ponds, and anaerobic cultures.
Biological digestion of organic waste material is affected by the oxygen level present in the culture because the oxygen level determines the metabolic pathway available to the microorganism. Aerobic conditions provide plenty of oxygen to the culture, and fosters the growth of microorganisms that can use the exogenous oxygen as a terminal electron acceptor in the oxidation of organic acids generated from the metabolic breakdown of organic material. If insufficient exogenous oxygen is available to the culture, the conditions are anaerobic. Under anaerobic conditions, the absence of oxygen as a terminal electron acceptor results in the excretion of organic acids into the culture medium as waste. The accumulation of acids in the culture medium can rise to toxic levels for the organisms if the pH of the culture is not regulated by some method of acid oxidation such as methane fermentation. Many types of bacteria, called facultative bacteria, can live under both aerobic and anaerobic conditions.
Anoxic conditions exist where essentially no oxygen is available to the culture. Under anoxic conditions, the growth of microorganisms is fostered that can utilize nitrogen as an electron acceptor in the absence of oxygen. Anoxic cultures convert nitrate nitrogen into nitrogen gas in a process called anaerobic denitrification. Two classifications of nitrifying microorganisms have been identified. Nitrosomonas bacteria oxidize ammonia nitrogen to nitrite. Nitrobacter bacteria oxidize nitrite to nitrate. Both groups are chemoautotrophs.
In addition to organic material, wastewater also contains inorganic matter to be removed. The inorganic components of wastewater of principal concern to the present invention include nitrogen, phosphorous, and sulfur. Nitrogen can be removed by biological cultures under anoxic conditions as described above. Phosphorous is necessary for the growth of algae and bacteria, and is primarily removed from wastewater by incorporation into the cells of growing cultures, although care may be necessary to avoid undesirable noxious algal blooms in the presence of excess phosphorous. Phosphorous may also be removed by chemical precipitation whereby soluble phosphorous is incorporated into an insoluble complex and allowed to settle as solid sediment. The present invention does not utilize chemical precipitation.
Sulfur, in the form of sulfate ion, occurs naturally in most water supplies and is common in wastewater as well. Sulfur is required for protein synthesis and is released by protein degradation. Under anaerobic conditions, sulfates are reduced to sulfites and hydrogen sulfide by anaerobic bacteria. Hydrogen sulfide can even be biologically oxidized to sulfuric acid.
The primary activity of biological cultures in the treatment of wastewater is the bio-removal of organic material. To measure the effectiveness of the treatment, it is necessary to estimate the amount of organic waste susceptible to biological removal. The total organic content of wastewater can be estimated by measuring the amount of oxygen required for chemical conversion of all the organic material into carbon dioxide and water. This is referred to as the Chemical Oxygen Demand (COD). Another measure is the Total Organic Carbon (TOC), which measures the carbon dioxide produced by combustion. The portion of the total organics susceptible to bio-conversion is referred to as Biological oxygen Demand (BOD). BOD can be measured by direct measurement of the oxygen uptake due to the biological action on the organic material the wastewater, or by calculating the change in the amount of organic material as measured by COD or TOC due to biological activity. BOD is known to those skilled in the art as an important measure of effluent quality.
The cell mass concentration of a biological culture is referred to as mixed-liquor suspended-solids (MLSS). It is known to those of ordinary skill in the art that biological water treatment cultures comprise a mixture of a variety of microorganisms. Although the culture conditions are established to foster a particular biological process, no culture in the field is perfectly homogenous with regard to the population of microorganisms inhabiting the culture. As a result, different processes are occurring in different areas of any given culture, even though one particular process is dominant. For example, an aerobic culture may utilize bubblers to supply exogenous oxygen to the facultative microorganisms in the culture, but the oxygen so supplied may not be uniformly available throughout the culture so that zones of reduced oxygenation may exist, between the bubblers, for instance, creating an anaerobic or even anoxic subzone within the primary culture. The present invention takes advantage of this characteristic of biological cultures to provide thorough processing of the waste material in the treated water.
While others have proposed methods for the treatment of agricultural wastewater using biological cultures, the present invention does not require the use of chemicals to precipitate solids from the wastewater, nor does it require the use of skimmers, geo-reactors, or other additional steps or processes.
For example, in U.S. Pat. No. 5,545,325 a facility for combined aerobic and anaerobic treatment of livestock wastewater is disclosed. This is accomplished with a natural solid-liquid separation device comprising a digester with an automatic skimmer installed at the upper part of the digester, and a level sensing control valve to control the volume of wastewater in the digester.
In U.S. Pat. No. 5,480,548 a wastewater purification process is disclosed including directing the wastewater through at least one aerobic zone and at least one anaerobic zone in repeating or alternating segments. A portion of effluent from the one or more anoxic zones are fed through at least one aerobic zone to which wastewater is fed and returned to the upstream portion of the anoxic zone.
In U.S. Pat. No. 5,472,472 a process for the bio-conversion of soluble and suspended organics from animal waste is disclosed wherein the wastewater is treated through a series of eco-reactors and bio-reactors, including aerobic and anaerobic treatment. Soluble phosphorus is precipitated with metallic salts.
In U.S. Pat. No. 4,824,563 a method of treating high concentration organic wastewater in dependence upon micro-organisms is disclosed. The method includes an anaerobic operation tank, an aerobic tank, and an ozone treatment tank.
In U.S. Pat. No. 4,999,111 a process for treating wastewater is disclosed including aerobic, anaerobic, and anoxic treatment. The process of the '111 patent includes splitting the stream of wastewater into a main stream and a side stream wherein the anoxic treatment takes place in the side stream. Activated sludge is generated in the side stream and is recycled to the main stream treatment process that includes at least one aerobic treatment zone.
The present invention addresses problems associated with the treatment of wastewater, and particularly wastewater having a high level of organic material such as, for example, wastewater from high volume livestock production, with an apparatus to produce treated water suitable for irrigation, a portion of which may be recycled to the livestock production site for flushing waste.
Thus it is an object of the invention to provide a facility for removing solid residues from wastewater and to reclaim the solids for the food value therein.
It is another object to essentially remove the soluble organic components from industrial and agricultural wastewater.
It is another object to remove ammonia and urea from the recycle water being pumped to a livestock house for floor flushing, contributing to better health for the livestock occupying the livestock house.
It is another object of the invention to significantly reduce the total nitrogen in the treated wastewater being used for irrigating enabling the production of more economical cash crops.
It is another object of the invention to remove the soluble phosphorus from the irrigation water, when required.
It is another object of the invention to provide a wastewater treatment apparatus that is more efficient, requiring less land than is currently practiced.
It is another object of the invention to provide a facility for the treatment of agricultural or industrial wastewater that may utilize either lagoons or above surface basins or tanks.
It is another object of the invention to provide a method and apparatus to treat animal waste from high volume livestock production so that said waste is disposed of in an ecologically benign fashion.
It is another object of the invention to provide treated wastewater that is environmentally safe.
These and other objects and advantages will be apparent from the following description of the invention.